George Osborne has defended the role of HSBC as a “very important bank” for Britain as he once again dodged questions about the extent of his discussions about tax evasion at its Swiss arm.

The chancellor made a plea on behalf of HSBC after repeatedly failing to answer questions about his conversations with Stephen Green, the bank’s former boss. Lord Green was appointed as a Conservative trade minister in 2011 – some time after the first allegations about tax evasion by wealthy HSBC clients in Switzerland began to emerge.

Speaking on BBC Radio 4’s Today programme, Osborne was pressed on whether he had ever spoken to Green about tax evasion at HSBC Suisse. At first, Osborne would only answer a different question, saying Green had been through “proper procedures”. This tactic is the same as the one used by David Cameron, who is also refusing to say whether he discussed tax evasion by HSBC clients with Green.

Osborne then changed tack, arguing it had not been alleged that HSBC Suisse was complicit in the tax-evading activities of its clients at the time of Green’s appointment.

“The information that has been published recently has only recently come to light. Until that point, the allegations had been that individuals with bank accounts at HSBC had been evading tax and HMRC was, rightly, investigating it. The new information is that, potentially, the allegation is that HSBC Suisse colluded in this – this is new information,” he said.

Osborne then appeared to try to deflect the conversation by making the case for HSBC to be given a chance to move on from the scandal.

He said: “Can I just make a point? It’s absolutely essential that this is dealt with, that HSBC, as they’ve said themselves, deal with the problems. HSBC are also a very important bank for our country, it employs 50,000 people, many of whom will be listening to this programme.

“So we want the bank to deal with these problems, to deal with the legacy of the past and have a bright and successful future and we mustn’t entirely ignore the fact that Britain does need successful and strong companies going forward.”

Both Cameron and Osborne have been under pressure about HSBC following revelations last month by the Guardian, the BBC and international media outlets about the extent of evasion by clients of the Swiss subsidiary and the bank’s role in enabling this to happen.

Only one person in the UK has been prosecuted so far, while around 1,000 have been allowed to pay up and therefore escape court.

Downing Street has so far refused to hold an inquiry into HMRC’s decisions or review its prosecution policy.

Speaking on Wednesday morning, Osborne repeated his previous assertion that he could not get involved in prosecutions but said he was looking at further changes to the law to make it easier to bring criminal charges against tax evaders in the future.

“If there are deficiencies in the law, if it’s difficult to bring these prosecutions then we should change the law ... My responsibility is to make sure the law is correct, that these authorities have the resources they need to do their job – and they’ve told me that they do have their resources. We are looking at further changes to the law to make sure we have a tough regime.”

Ed Balls, the shadow chancellor, said Osborne was “asked six times whether he discussed allegations of tax evasion at HSBC with Lord Green, the bank’s former chairman, and six times he refused to answer”.

He said: “What has George Osborne got to hide? People will draw their own conclusions from his total failure to answer.

“The chancellor also struggled to explain why, since the government received these files in May 2010, only one person has been prosecuted out of 1,100 names.

“David Cameron and George Osborne must now come clean about their discussions with Lord Green – both while he was a Tory minister and before they appointed him.”